In social networks, many applications and spreading depend on the nodes with high influence to do viral marketing, which indicates that nodes' influence should be measured in a comprehensive and reasonable way. The appearance of fake fans results in change of network topology and brings new challenge to topology-based traditional methods. This paper incorporates both the network topology and interactions among nodes into our new distribution mechanism of node influence calculation in social networks. Considering the similarity of node behaviors in time domain and several key factors, this paper presents by a discounted Bayesian model for direct influence between nodes at first. Then a semi-ring-based aggregation implements for indirect influence and the composite influence are obtained by the combination of both direct and indirect influences. Simulation shows that this mechanism not only performs well against fake fans attack and restrains the fluctuation of nodes' influence, but also spreads to more nodes when we choose several nodes with high influence under our method to be source nodes.
Adaptive network is characterized by feedback loop between states of nodes and topology of the network. In this paper, for adaptive epidemic spreading model, epidemic spreading dynamics is studied by using a nonlinear differential dynamic system. The local stability and bifurcation behavior of the equilibrium in this network model are investigated and all kinds of bifurcation point formula are obtained by analyzing its corresponding characteristic equation of Jacobian matrix of the nonlinear system. It is shown that, when the epidemic threshold is less than epidemic persistence threshold R00c, the disease always dies out and the disease-free equilibrium is asymptotically locally stable. If R0c01, a backward bifurcation leading to bistability possibly occurs, and there are possibly three equilibria: a stable disease-free equilibrium, a larger stable endemic equilibrium, and a smaller unstable endemic equilibrium. If R01, the disease is uniformly persistent and only one endemic equilibrium is asymptotically locally stable. It is also found that the system has saddle-node bifurcation, transcritical bifurcation, and Hopf bifurcation. Numerical simulations are given to verify the results of theoretical analysis.
A novel finite-difference time domain (FDTD) algorithm named equivalent circuit FDTD (EC-FDTD) is realized, which introduces lumped elements from transmission line theory into Yee cell. It includes lumped elements such as series inductance and shunt capacitance in the right-handed materials, as well as shunt inductance and series capacitance in the left-handed materials. Due to its promising physical thoughts, it can be easily generalized to arbitrary dispersive materials including frequency selective surfaces and metamaterials. The technology of streaming single-instruction multiple-data (SIMD) extensions (SSE) was proposed by Intel and is currently utilized in personal computers. SSE is a kind of parallel speedup technology in one core. The speedup can be achieved four times in principle without changing hardware. Combined with SSE, the EC-FDTD can be apparently accelerated. Twice speedup is achieved in the tests of this paper. The algorithm of EC-FDTD is utilized to design the wideband metamaterials absorbers by employing the single square and double square loops loaded with the lumped resistors. The invisible radome has a great impact on reducing the radar cross section of the antenna out of band. The radome is designed with operating frequency to be 1 GHz and the absent bandwidth from 3 GHz to 9 GHz by the algorithm. And then these prototypes are fabricated and measured. From the comparative results, the correctness of EC-FDTD and the speedup of the SSE are both verified.
The three-dimensional (3D) dynamics of a projectile in granular media is simulated using DEM (discrete element method). Periodic boundary conditions are adopted, and the effects of gravity, contact forces, damping and friction are taken into account. The 3D simulation results fit the experiment results very well. Simulation results show that the heaver the projectile, the deeper the penetration depth. The impact depth grows linearly when the projectile quality increases. And when the density of granular media decreases, the penetration depth also increases. Splash of granular particles is also observed in the impact simulation.
According to the general shallow water equations, the nondimensional nonlinear dynamic equations are obtained that can describe large-scale barotropic atmosphere. Using multi-scale method, a nonlinear controlling equation for disturbed height (or pressure) field is deduced. Applying elliptic equation to construct the solutions of the controlling equation, the analytic solutions of the disturbed height field and velocity are obtained, which include the multiply periodic waves and shock (explosive) waves. The solutions of the disturbed height field present periodic waves with different periodicity and wavelength along longitude and latitude, which are modulated by the solitary waves of latitude. The velocity solutions display that in the large-scale air flows exist periodic distribution phenomena of cyclone and anticyclone.
The geometrical quantum discord (GQD) is an effective measure of quantum correlation in quantum systems. We investigate the dynamics of quantum correlation between two atoms in a damping Jaynes-Cummings (J-C) model according to the geometrical quantum discord. The evolutional characteristics of GQD are given for both the resonant and non-resonant cases; moreover, the effect of damping on GQD is revealed.
We have deduced a two-level form of beam evolution in photonic lattices of semiconductor photorefractive medium and its classical canonical form of the two-level equation. We analytically calculate the fixed points of the classical canonical aligns, analyze its stability and calculate the critical value of topology changes. According to the classical canonical form of the two-level equation, we make space phase diagram, further analyze the self-trapping of beam propagation in semiconductor photorefractive medium and find two kinds of self-trapping: 1) Both the population difference and the relative phase in energy levels oscillate near an equilibrium point in the phase space. 2) The population difference in energy levels oscillate near an equilibrium point while the relative phase increases monotonously. From the three aspects of high frequency, low frequency, and intermediate frequency, we investigate how an external periodic field influences the self-trapping and find that the external high frequency periodic field may dramatically modulate the critical points at which the transition to self-trapping occurs. It makes the self-trapping occur with small nonlinear effect when the beam propagates in semiconductor photorefractive medium.
We suggest a combined modulation quantum key distribution (QKD) system which encodes each single-photon signal with both phase modulation and polarization modulation. With the aid of dual-velocity protocol of hybrid QKD system, we construct a scheme to realize this combined modulation QKD which generates two-bit key with one signal for increasing the efficiency of QKD. We also develop a combined modulation Michelson QKD system, then solve the stability problem of the combined modulation QKD system in principle.
This paper puts forward a quantum signaling switch model. The quantum signaling switch consists of a classical information control module, an exchange control module and a quantum exchange module. Classical control module transmits the initial entangled state information to the entanglement measurement and switching unit and updates the routing information. Exchange control module will choose the path, and is ready for the distribution channel of the entanglement photons. The quantum exchange module generates quantum entanglement pairs, measures the Bell state and achieves entanglement swapping. Quantum signaling switches can realize multi-user communication and local area network communication. Through the performance analysis and simulation of the switch, the results show that the switch is simple in structure, secure and easy to expand; also the time delay is small. This will be helpful for the construction of the quantum communication network.
Studying quantum correlation dynamics of a central two-qubit system coupled to Ising chain model, we obtain that the evolution of quantum discord and geometric measure of quantum discord for the central atoms. We find that quantum correlation exists a sudden transition in the weak coupled interaction near the quantum critical point of Ising chain. Moreover, the evolution of geometric measure of quantum discord in invariant to some extent.
We find a new approach to study nice error bases and quantum error-correcting codes, namely the group algebra which gives us an algebraic notation for nice error bases and quantum codes. From this algebraic notation we establish a series of linear programming bounds on the most general quantum error-correcting codes.
The Landau damping and frequency-shift of monopole mode in an elongated-rubidium Bose-Einstein condensate are investigated by using the time-dependent Hartree-Fock-Bogoliubov approximation. Improving the previous approach, We have taken into account the practical relaxations of elementary excitations and the orthogonal relation among them. With such an approach, we provide a new calculation formula for Landau damping rate and frequency-shift. In addition, our previous method of eliminating the divergence in three-mode coupling matrix elements is also improved by zeroing the kinetic energy at the condensate boundary instead of minimizing the ground-state energy. Based on these improvements, both the Landau damping rate and the frequency-shift of the monopole mode are analytically calculated and their temperature dependences are also discussed. And all the theoretical results are in agree meat with experimental data.
The change of phase space and periodic modulation of Fermi gas from the BCS to unitarity is investigated in one-dimensional optical lattice. Through controlling the scattering length and coupling constant in unitarity, we find the critical values (from the Josephson oscillation to the oscillating-phase-type self-trapping and from the latter to the self-trapping), at the same time, we also find the relationship between the critical coupling constants and the scattering length.
In this paper, a novel method, to synchronize two identical or different chaotic/hyperchaotic systems with variable coefficients, is proposed based on the strictly positive real transfer function matrix. By adding a synchronization controller to the response system, the nonlinear parts of the error system derived from the synchronized systems are identified as the inputs of the error system, and the error state variables are identified as the outputs of the error system. Then the transfer function matrix of the error system can be strictly positive real. As a result, the error system can be asymptotically stable at the origin, i.e., the two chaotic/hyperchaotic systems can reach stable synchronization. Moreover, the designed synchronization controllers are linear, clear in parameter selections and robust to the changes of the coefficients of the error system. The specific design processes of the synchronization controllers and the corresponding results are presented in the paper. Also, the numerical simulation results are given to verify the feasibility and effectiveness of this method.
Due to the strong nonlinearity of the Buck converter, it can be in the chaotic state under certain parameters and the chaotic Buck converter does not work normally. In order to suppress the chaotic phenomena in the Buck converter, a chaotic control scheme is demonstrated by establishing the accurate state equation models, and then analyzing the controllable range diagrams, the switching logic diagrams, the phase portrait, the inductor current waveforms and the output voltage waveforms. Also this scheme can be implemented by improving the correlation between the inductor current and the output voltage of the Buck converter. Research results show that this scheme can stabilize the chaotic Buck converter to the period-1, period-2, period-4, period-8 orbits, without determining the desired targeting orbits in advance. Moreover, this scheme does not depend on circuit parameters of the Buck converter, it only depends on an external parameter named the coupling strength, so this scheme can be applied to the other power converters.
In this paper, from the stability theory of fractional-order chaotic system, a kind of dislocated projective synchronization for fractional-order Chua's system is successfully completed through a nonlinear controller. Meanwhile, the fractional-order unit circuit is designed, according to the series-parallel structure of resistor-capacitor and the approximate linear transfer function expression for the complex frequency domain. Thus, non-inductive modular circuit of dislocated projective synchronization of fractional-order Chua's system is realized. The circuit simulation results prove the feasibility of the scheme. Furthermore, the method can be applied in secure communication through the improved chaotic masking. The information signal can be concealed and recovered. Numerical simulation results show the effectiveness of the proposed method.
Bidirectional ring-coupled Duffing oscillator hasbeen investigated. A phenomenon is discovered, showing that when one of the oscillators is driven by pulsed signal under certain parameter conditions, this and the other oscillators will suddenly change from synchronization to transient non-synchronization and then rapidly return to synchronization, which is defined as transient synchronization mutation in this paper. This phenomenon is used to accurately detect partial discharge signal in strong noise environments. The experimental tests show that this method achieves good detection effect in low SNR for partial discharge signal of different discharge electrode, which can further extend the weak signal detection range based on Duffing oscillator.
In order to apply carbon nanotube field effect transistor (CNTFET) to circuit simulation, maintaining an acceptable accuracy while minimizing computation time is a major problem. To establish a simple and high accuracy CNTFET model in HSPICE, based on the semi-classical model of CNTFET, the relationship between self-consistent electric potential and carrier density is analyzed, linear approximation is used for curve fitting, and explicit expression of self-consistent electric potential is deduced, so that the iterative solution of an integral equation is avoided. Then the CNTFET model in HSPICE is built. Simulation demonstrates that the proposed model can maintain high accuracy, and the logic functions can be realized in corresponding logic gates built with the proposed model, while the computation time is significantly reduced.
Using Melnikov method we have analysed and calculated the homoclinic orbits of a slowly varying oscillator, derived from the T chaotic system with generalized Hamiltonian structure under periodic parametric perturbation. Also the parameter bifurcation conditions of homoclinic orbits are obtained. The simulation results demonstrate the feasibility of periodic parametric perturbation control technology, and the correctness of the discussion in this paper.
Magnetic field and temperature dependence of Sagnac interferometers consisting of birefringent magneto-optic fibers is investigated. Experimental results show that the transmission spectrum of the all-fiber Sagnac interferometer moves towards the shorter wavelength side with the increase in temperature (temperature coefficient -0.435 nm/℃), and the transmissivity becomes wavelength- insensitive for a larger magnetic induction. And then, the temperature-insensitive magnetic field measurement is achieved by adjusting the polarization controller within the interferometer, and the magnetic field coefficient is 189 mW/T2 in the experiment, which is in agreement with the theoretical results.
Utilizing insulator-metal phase transition of vanadium dioxide thin film, we propose a thermally controlled terahertz modulator based on metamaterial, and research the transmission characteristics and temperature tunable characteristics of phase transition in metamaterials in THz wave band. While the incident THz wave is of horizontal polarization or vertical polarization, two independent pass bands are generated near 1 THz. The center frequencies of the two pass bands are 1.3 THz and 1.7 THz, the bandwidths of them are 0.2 THz and 0.35 THz. In addition, when temperature rises from 40℃ to 80℃, the transmissions of the two pass bands drop apparently, especially at phase transition temperature of 68℃. For the two polarization states, the modulation depths achieve 60% or more, which is the great function of a modulator.
In this paper, we demonstrate a method of atmospheric CO2 vertical column density (VCD) retrieval by using weighting function modified differential optical absorption spectroscopy (WFM-DOAS). Direct sun measurement serves as an example for WFM-DOAS fitting. The atmosphere is divided into 50 layers in the process of WFM-DOAS retrieval, while the simulated sun-normalized radiance and the total weighting functions (CO2, H2O and CH4) for each measurement are computed in terms of the radiative transfer model (RTM) SCIATRAN by using the HITRAN data base and the solar spectrum from Livingston and Wallace (1991). The CO2 vertical column density time series were obtained by utilizing WFM-DOAS fitting method to all direct sun measurement spectra. Fitting errors are all less than 3%. Fitting results for two different DOAS algorithms are compared with each other. It is indicated that the WFM-DOAS technique has the potential of being applied in passive gas remote sensing in the infrared region.
Thin films of 0.65PMN-0.35PT PMN=Pb (Mg1/3Nb2/3)O3 and PT=PbTiO3 with a thickness about 250 nm were prepared on LaNiO3/SiO2/Si substrates by radio frequency magnetron sputtering. The films were annealed using high pressure annealing (HPA) technique in oxygen atmosphere. Effect of HPA on the crystal structure, morphology and electrical properties of the films was studied. XRD patterns of the films indicated that PMN-PT films treated by HPA in oxygen atmosphere (annealing temperature 400℃) showed a pure perovskite phase, with highly (100) preferred orientation. The strong and sharp diffraction peak showed the better crystallization of PMN-PT thin films after HPA. SEM observations showed that a rod or bubble morphology was present on the films surface. Ferroelectric properties tests showed that the PMN-PT film annealed in oxygen atmosphere at a pressure of 4 MPa, and annealing time of 4 h had good ferroelectric properties, in which the remanent polarization (Pr) could reach 10.544 uC/cm2. The shape of electric hysteresis was better, but the leakage current was too large, which may be due to the microstructure of the films. Meanwhile, the dielectric tests indicated that PMN-PT thin films could show very good dielectric properties, and the dielectric constant (r) could reach 913, and dielectric loss (tg) was very small, only 0.065.
The results obtained by using finite time thermodynamics (FTT) are universal and have become one of important foundations of thermo-physics. A large number of researches have been carried out in the performance optimizations and optimal configurations of single-and multi-stage two-heat-reservoir direct and inverse thermodynamic cycles by using FTT. The obtained new results have more important practical significance for engineering design and optimization than those obtained by using classical thermodynamics. This paper reviews the new advances of the optimal performances and optimal configurations of single and multi-stage two-heat-reservoir direct and inverse thermodynamic cycles following different heat transfer laws, including the new advances of the optimal performances of endoreversible and irreversible Carnot heat engine, Carnot refrigerator and Carnot heat pump cycles under different heat transfer laws, and the new advances of the optimal configurations of two-heat-reservoir heat engine, refrigerator and heat pump cycles, as well as multi-stage complex thermodynamic cycles with different heat transfer laws.
Nuclear structure phase transitions SU(3)–U(5)–SU(3) of the yrast-band structure in 182Os nucleus are successfully described, based on the association of microscopic interacting Boson model (IBM) with the γ-ray energy on spin curves (E-GOS). It is very abstract because of lack of concrete facts. A probable explanation of these one after the other phase transitions are geometrically given, with a functional relation of microscopic parameters in microscopic sdIBM-Fmax approach and potential energy surface in Bohr collective model. It is expounded that at high angular momentum, in a well-deformed nucleus, a probable way to the γ-vibrational energy can become lower than the rotational energy bcause there are a number of degeneracy states formed by quantum effect between the highter and lower excition states so as to achieve SU(3)–U(5) structue phase transition.
Many of the stable nuclei at the neutron-deficient side of the beta-stability valley cannot be synthesized in the neutron-capture processes. The origin of the so-called p-nuclei has been a long standing question in the nuclear astrophysics. The rapid-proton capture process (rp-process) proposed in the 1980s was one of the possible mechanisms to be responsible for some light p-nuclei. In this work, a model for rapid-proton capture process (rp-process), within the (p,)-(,p) equilibrium approximation, is established. In the framework of this model, the influence of astrophysical conditions (i.e., proton number density, temperature, and proton irradiation time) on the rp-abundance pattern is investigated. In addition, the recent-measured mass data of neutron-deficient atomic nuclei by using the storage ring mass spectrometry at IMP, Lanzhou, are employed in our calculation. It is found that the abundance at A=41 is increased by two orders of magnitude when using the new by determined mass of 41Ti, while the uncertainty of the computed abundance is reduced by almost two orders of magnitude.
A cesium atomic magnetometer based on laser-pumped rf resonance has been investigated and demonstrated experimentally. Atoms are polarized and pumped to dark states by circularly polarized light. When there exists a magnetic field, the corresponding magnetization will be precessing around the magnetic field at Larmor frequency. By means of adding a resonant rf magnetic field, the atoms will be depolarized and absorb photons again. By detecting the spectrum of the transmitted light, one can obtain the information about the external magnetic field. We build an 894nm external cavity diode laser with a frequency stabilization device, and a low noise magnetic field measurement environment. After the optimization of the magnetometer parameter and closed-loop measurement, an ultimate sensitivity of 19 fT/Hz1/2 and an intrinsic sensitivity of 1.8 pT/Hz1/2 have been achieved with the spatial resolution smaller than 2 cm.
The characteristic properties including equilibrium lattice constants, elastic constants, cohesive energies and alloy formation energies, of stoichiometric L12 type NiAl3, L12 type Ni3Al, L10 type NiAl and B2 type NiAl, are calculated using a constructed n-body potential model combined with molecular dynamics. Furthermore, the types of point defects in the ordered NixAl1-x (x=0.25, 0.5, 0.75) systems in the nonstoichiometric case are discussed, to validate the model. The present calculation shows that the point defects are the antisites. It is in good agreement with other investigations. Then the n-body potential calculations are performed to investigate the site preference of ternary elements Mo/Ta/W alloying additions in the NixAl1-x systems. The occupation site of the ternary elements are analyzed based on the occupational energy minimizing. And the results show obviously that the occupational sites of Mo/Ta/W are the Al site.
The cluster size is an important parameter in the study on the interaction of intense laser pulse with cluster jet produced by the gas adiabatic expansion through a nozzle into vacuum. The Hagena scaling law is usually used to estimate the average cluster size. However, there is the deviation of average cluster size from the prediction by the scaling law in the case that the conical nozzle is used at the high gas backing pressure. In this work, firstly the equivalent diameter of conical nozzle is re-calculated in detail, and then the relation between deq and the radial dimension of the cluster jet is obtained. As an example, the images of Rayleigh scattering light by argon cluster jet at different backing pressures are recorded to investigate the dimensions of cluster jet. And then the corresponding theoretical dimensions based on the idealized straight streamline model in the scaling law are compared with the experimental dimensions. It is found that the experimental dimension is larger than the theoretical one, and is related to the gas backing pressure. This under-estimation of theoretical cluster jet dimension leads to the over-estimation of the equivalent diameter of conical nozzle which is responsible for the cluster size deviation in Hagena scaling laws.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Waveguide discontinuities with anisotropic dielectric are simulated and analyzed by the precise integration method. The discrete coefficient matrices for the cross-section of the waveguide, which contains anisotropic dielectric, are deduced from the variational principle based on single variable corresponding to the vector wave equation. Introducing the dual-variables, the stiff matrices are calculated by using precise integration method in a Hamiltonion system. Then the problem is solved by assembling the finite elements. Numerical results show accuracy and good efficiency of the method. The influence of the components of permittivity and permeability on the waveguide transmission characteristic is also discussed.
Multiband and broadband metamaterial absorbers have been proposed in the paper. The proposed absorbers are composed of metallic copper patterns on both sides of a dielectric layer. One side consists of metallic circular patches and metallic annular patches, and the other side is of metallic ground plane. Each distinct metallic circular patch unit cell or annular patch unit cell has one distinct resonant peak in a very narrow band, and these unit cells are independent of one an other. Therefore, combining two different unit cells which resonates at different frequencies can obtain dual-band absorber. Based on the theory, combining three different unit cells can obtain tri-band absorber, and combining four different unit cells can obtain the absorber which resonates at four different frequencies. In addition, the electric field distribution verifies that each distinct unit cell resonates at a different frequency. Broadband metamaterial absorber can be obtained according to the optimized combination of the different unit cells. Increasing the number of different unit cells broadens the frequency range when their resonances are closely packed together, thereby resulting in a broadband resonance.
The line focusing characteristics of axicon illuminated by non-diffracting Bessel beam was analyzed in terms of Hankel theory and diffraction integral theory, and a new kind of method to generate periodic bottle beam was put forward, i.e. Talbot effect bottle beam was generated by axicon illuminated by non-diffracting Bessel beam. Intensity distributions along the propagation path and the intensity evolution of the bottle beams in a complete period after the axicon illuminated by non-diffracting Bessel beam were simulated numerically. An optical system was designed and Bessel-like beam was obtained by light wave emitted from He-Ne laser passing through axicon after the optical system, and then an axicon was used to focus the Bessel-like beam. Periodic bottle beam was then observed after the axicon, and the spot diagram of two periodics were taken by a CCD camera. Experimental results agree well with the theoretical analysis. This result has a practical significance in multi-plane micro-manipulation and may serve as a guideline in optical micro-control by periodic bottle beam.
The experimental demonstration of polarization-independent reflection structure that consists of two magneto-optical crystals and two mirrors is reported. According to the characteristics of polarization compensation, the reflection structure was simplified in this paper. A single magneto-optical crystal and two mirrors reflection structure is presented to simplify the polarization-independent reflection structure. The experiment shows that the degrees of polarization maintenance of the two reflection structures are both higher than 99.97%. By way of contrast, the polarization states of 90° reflection laser of single mirror and two mirrors are measured. Under these conditions, the degrees of polarization maintenance of mirrors are 92.1% and 76.2%, respectively.
Based on the methods of vector angular spectrum of electromagnetic beams and stationary phase, the analytical expressions of TE and TM terms and energy flux distributions of cosh-Gaussian (ChG) vortex beams in the far field are derived, and used to study the phase singularities and energy flux distributions of the ChG vortex beams. It is shown that the density and position of optical vortices will vary by changing decentered parameter or waist width in the ChG vortex beams. The vortex off-axis distance leads to an asymmetric spatial distribution of energy flux. With gradually increasing vortex off-axis distance, dark spots around the origin will move toward the origin center.
A novel phase measurement method based on the schlieren apparatus is proposed, and the ultrafast phase evolution of the ejected material generated during the femtosecond laser ablation of aluminum is experimentally studied by this method. Different from the conventional schlieren technique, the phase measurement method presented in this work uses coherent light as the illuminating light. The specimen's phase under-test is derived with the help of the interference between the light which irradiates the surroundings of the specimen and the light which transmits through the specimen and diffracts on the razor edge of the schlieren apparatus. One remarkable merit of this method is that it can clearly exhibit the specimen's phase variation of mπ or 2mπ (m is an integer). The ultrafast process of the ejected material generated during the 5.4 J/cm2, 50 fs laser pulses ablation of the aluminum target is investigated by this novel phase measurement method and the pump-probe technique. Results show that the ejected material is composed of three sequentially appearing regions with different phase evolving processes, which are respectively corresponding to the ejected plasma-state material, the successively ejected material normal to the target surface and the shock wave. It is also found that during the time interval of 0–9.0 ns after the femtosecond pulse strikes the target, the phase of the ejected plasma-state material varies beyond π due to the expansion and recombination, but the phase variation of the successively ejected material does not exceed π.
The accurate localization of iris center is difficult since the outer boundary of iris is often occluded significantly by the eyelids. In order to solve this problem, an infrared light source un-coaxial with the camera is used to produce dark pupil image for pupil center estimation. Firstly, the 3D position of the center of cornea curvature, which is used as translational movement information of eyeball, is computed using two cameras and the coordinates of two cornea reflections on the cameras' imaging planes. Then, the relative displacement of pupil center from the projection of the cornea curvature center on 2D image is extracted, describing the rotational movement of the eyeball. Finally, the feature vector is mapped into coordinates of gazing point on the screen using artificial neural network. As for the eye region detection problem, two wide-view webcams are used, and adaptive boosting+active appearance model algorithm is adopted to limit the region of interest within a small area. The result of our experiment shows that the average root-mean-square error is 0.62 in horizontal direction and 1.05 in vertical direction, which demonstrates the effectiveness of our solution in eye gaze tracking.
Inspired by the wavelet transform in quantum mechanics, we define the new Ridgelet transform for quantum optics by rewriting the classic Ridgelet transform via the two-mode coordinate representation in Fock space. Furthermore, we give the explicit form of the asymmetric operator's integral and derive two useful formulas for the normal ordering of the two-mode operator with the help of the technique of integration within an ordered product (IWOP) of operators. By choosing the two-variable Mexican hat's mother wavelet function, we analyse the Ridgelet transforms of the coherent state, special squeezed coherent state, intermediary entangled state on the basis of the theories we have mentioned.
A full quantum theory is adopted to derive the differential equations satisfied by the state of a system that is composed of an electron tunneling-coupled quantum-dot molecule interacting with a single-mode radiation field. The phase of the field is calculated by the Pegg-Barnett quantum phase formalism under the initial condition of a coherent-state field and the tunneling excited state or ground state for the quantum-dot molecule. Phase distribution and fluctuation of the field are analyzed, the influence of interaction between phonons and the quantum-dot molecule on the Pegg-Barnett quantum phase is investigated, and the phase distribution is compared with the Husimi phase distribution of the field. Results indicate that temperature can have a marked impact on the phase evolution. The existence of phonons suppresses the field phase distribution and fluctuation in the case when the quantum dot molecule is initially in the tunneling-excited state, while it enhances the diffusion and fluctuation of the field phase in the case when the quantum dot molecule is initially in the ground state. The Husimi phase distribution and the Pegg-Barnett phase distribution agree with each other fairly well in our study.
Based on the time serial signal generated by power spectrum density inversion, the closed-loop compensation residual variances of tracking loop and high-order error correction loop with finite error rejection -3 dB bandwidth and time delay are simulated. The data fitting results of relationships between residual variances and corresponding error rejection -3 dB bandwidths are obtained. The system effective bandwidths are modified so as to make the estimate of residual variances more precise.
A novel photonic crystal (PC) all-optical switch based on the shift of defect mode is demonstrated. Two photonic crystal waveguides are connected by a photonic crystal cavity. The point defect of the photonic crystal cavity is filled with phenylacetylene liquid cyrstals intermingled with azobenzene. The output of the optical switch is controlled by adjusting the rotation angle of the liquid crystals' orientation vector. And the optical switch is numerically investigated by using the finite difference time domain (FDTD) method and plane wave expansion method. Numerical simulation shows that the optical switch based on the PC cavity can be changed by adjusting the applied linearly polarized light. Results show that the switch has low threshold power density, great extinction ratio, and small size.
Non-imaging reflector may present the advantage to eliminate the dark image in beam down 2-stage optical concentrator. The working principle of the non-imaging secondary (NIS) for an axial symmetric concentrator is revealed. The geometrical shape of NIS can generally be high order surface not restricted to the quadratic one in imaging optics or the CPC in non-imaging optics. The article has described the method to determine the parameters of the curve. To break the tradition in optics, we have demonstrated in the article that beside the quadratic curve, cubic curve can be equally used to form NIS. In the respect of solar energy application, we have made the discussion on the behavior of NIS for solar disc effect and how a new parameter can be used to optimize the design.
The characteristics of multi-point defect phononic crystal (PC) composed of square array of circular steel cylinders in water are investigated experimentally using the ultrasonic immersion transmission technique. The band structures of the PCs are obtained by the finite element method with 9×9 supercell approximation. A very good agreement with the experimental results, numerical transmission data and eigenmode frequencies of band structures is observe. Meanwhile the number of multi-point defects affects the localized modes of cavities and propagation characteristics, and the eigenmodes of defects show the symmetric or antisymmetric modes in designing the new type of acoustic wave devices.
In this paper, a novel locally resonant structure with composite units is proposed. Formation mechanisms and low-frequency characteristics of the band gaps in the proposed structure are investigated using finite element methods. Frequency positions of band gaps depend on natural frequencies of the corresponding locally resonant modes. And the gap width is related to both the Q factor of the locally resonant modes and the interaction strength in-between the locally resonant structural units. Phononic crystal structures with composite units exhibit multiple resonances and band gaps in low-frequency range, depending on the arrangement of locally resonant units. Due to the mode degeneracy of the vertical and horizontal local resonances, the composite structures possess band gaps below 200Hz with the total gap width more than 60% and the lowest frequency down to 18Hz. The structures and results provide a new effective method for phononic crystal structures to obtain broadband gaps in low-frequency range.
Taking into consideration the influence of bubble cluster secondary sound radiation, the dynamic equation of spherical bubble clusters is obtained for two bubble clusters co-existing in the same ultrasonic field. Based on the original dynamic equation, the resonance response characteristics of the two-bubble-cluster oscillation system in ultrasonic field are discussed. Results showed that there are two resonance frequencies in this system, that is, low resonance frequency and high resonance frequency, due to the interaction between oscillating bubbles in the bubble cluster, and the two resonance frequencies are related with the bubble's eigenfrequency. The eigenfrequency of the bubbles is related to the bubble cluster's initial radius, bubble cluster's size and the number of bubbles. The coupling between bubble free vibration and driving acoustic may arouse the bubble's forced vibration, whose amplitude and initial phase are related to the bubble initial radius, bubble number density and driving sonic frequency.
The vibration of bubbles in bubbly liquids has been studied when the driving sound field is fixed. The radius of the bubble will change when the bubble is driven by a driving acoustic field for a short time. This small change of radius is then fed back to the scattering process of the bubbles driven by the driving acoustic field. Thus the compound acoustic field including the scattered field of the bubble can be obtained. Then the bubble is again driven into vibration for a short time. By repeating the same procedure, the bubble vibration and its radius variation are simulated by a numerical method. It is shown that in the case of numerous bubbles in the liquid the vibration of a bubble is different from the case of only a single bubble in it. Because numerous bubbles will show interactions between one another, the radius of the bubble will change in different manner. For different size and content of bubbles, the radius of the bubble changes according to the following rules. The radius will oscillate in the vicinity of the equilibrium position; the radius oscillation shows a periodic cavitation process; the radius will vibrate during one cycle of cavitation; then, the radius will increase and oscillate in the vicinity of a certain value. Therefore, it is necessary that the bubble content should be considered in analyzing the vibration of the bubble in a bubbly liquid under a driving sound field.
In this paper, the experimental investigation of coherently combined air-modulated speakers is achieved. This paper addresses a basic architecture for coherent-combined air-modulated speakers by means of active phase control, and then the fundamental theory for coherent combination using stochastic parallel gradient descent algorithm is described. Numerical simulation on coherently combining sound sources with horn is carried out. Moreover, an experiment of far-field coherently combining two air-modulated speakers has been conducted, and the configuration scheme of parameters in practical terms is presented. Experimental results show that when the algorithm converges, the sound pressure level at the test spot is 4 dB higher than that of single source. A power spectrum analysis indicates that the sound power of coherently combining case is close to the sum of the sound powers between the coherently combining of the fundamental frequency components and the non-coherently combining of the other frequency components for all sound sources. Consequently, it is revealed that the acoustic wave phases for air-modulated speakers can be effectively controlled by the active phase control algorithm, and an evident coherent-combining effect is obtained.
A theoretical model is developed to investigate vibro-acoustic characteristics of shear deformable periodic stiffened laminated composite panels in mean flow, based on the first-order shear deformation theory (FSDT). The convected wave equation and boundary condition are used to account for the exact coupling effect between mean flow and laminated panel. Stiffeners interact with the laminated panel through both the normal line forces and torsional moments. Analytic formulations for the transverse displacement spectra and sound pressure level (SPL) are yielded by employing the Fourier wavenumber transform and the stationary phase method. The model is validated by comparing with existing public data. Excellent agreement is obtained. Numerical results show that the effects of shear deformation and torsional motion of the stiffeners cannot be ignored in high frequency range. SPL can be reduced by increasing the speed of mean flow; it is possible to avoid SPL peaks by altering the thickness and stiffener spacing.
Based on constructal theory, the constructal optimization of a disc on micro and nanoscales is carried out by taking minimum entransy dissipation rate as optimization objective; and the optimal construction of the disc with minimum dimensionless equivalent thermal resistance is obtained. The result shows that the optimal construction of the disc when the size effectis taken into account is obviously different from that without considering the size effect. There exists an optimal dimensionless channel length of the high conductivity material which leads to the minimum dimensionless equivalent thermal resistance. With the increase in the number of the elemental sectors, the minimum dimensionless equivalent thermal resistance decreases first and then increases, and there exists an optimal number of the elemental sectors which leads to the double minimum dimensionless equivalent thermal resistance, which is different from the performance characteristic of the disc on a conventional scale. The entransy dissipation rate of the disc, based on the minimization of entransy dissipation rate, is reduced by 7.31% as compared with that based on maximum temperature difference, that is, the average heat transfer temperature difference of the disc is reduced by 7.31%. The optimal construction on micro and nanoscales, obtained based on minimum entransy dissipation rate, can reduce the average heat transfer temperature difference of a disc, and improves its global heat transfer performance simultaneously. The work in this paper can help to further extend the application range of the entransy dissipation extremum principle.
The last decade has witnessed the explosive development of microfluidic systems. Droplet manipulation is one of the crucial technologies in design and optimization of microfluidic devices. In the present study, dissipative particle dynamics is applied to investigate the movement of a liquid droplet actuated by a constant force on structured substrate with different wetting properties ranging from hydrophilic to hydrophobic. By monitoring the variation of the advancing contact angle and the front position of droplet, the characteristics of the droplet motion is analyzed in detail. Results indicate that there exists an optimal structure for which the droplet has a largest speed. Additionally, the influences of wettability gradient, thermal fluctuation and external force are discussed. We find thermal fluctuation is helpful for the movement of droplet.
In this paper, we study the capillary flows in square tubes and in equilateral triangle tubes under microgravity condition by performing experiments in drop tower, and also compare them with those in circular tubes. Experimental results showned the influence of both size and shape of tubes on the capillary flow driven by interfacial forces. For tubes of the same shape, the influence of tube size is quite similar. Moreover, the capillary flows in square tubes and equilateral triangle tubes have some similarity with those in circular tubes with much smaller sizes. The results are helpful for understanding the capillary flows driven by interfacial forces with different parameters. And they are also useful for independently controlling the flow velocity and the volume flow rate by choosing appropriate tube shapes under microgravity condition.
Based on configucation theory, the construction of a “disc-point” heat transfer with cooling channels can be optimized by taking minimum entransy dissipation rate. Thus an optimal construction of the disc-shaped assembly with cooling channels is obtained. The results show that there exists an optimal aspect ratio of the elemental sector which leads to the minimum dimensionless equivalent thermal resistance of the elemental sector at the fixed pumping power; there also exists an optimal width ratio of the elemental and first-order cooling channel to the optimal dimensionless radius of the elemental sector, which leads to the minimum dimensionless equivalent thermal resistance of the first-order branched-pattern disc at the fixed total pumping power. Moreover, the optimal width ratio of the elemental and first-order cooling channels is only relative to the number of elemental tributaries. When the radius of the central disc tends to zero, the branch-pattern disc is simplified into a radial-pattern disc, and the radius of the first-order branch-pattern disc becomes the critical radius at this point. When the radius of the branch-pattern disc is higher than the critical radius, the branch-pattern design should be adopted, otherwise the radial-pattern design should be adopted. There exists an optimal number of elemental tributaries which lead to the minimum dimensionless equivalent thermal resistance of the first-order branch-pattern disc, which is obviously different from the results of the “disc-point” heat conduction constructional optimization with high-conductivity channels. The optimal constructions of the first-order branch-pattern disc based on the minimizations of entransy dissipation rate and maximum temperature difference are different. The dimensionless equivalent thermal resistance of the disc with cooling channels based on the minimization of entransy dissipation rate is greatly reduced as compared with that based on the minimization of maximum temperature difference, and its global heat transfer performance is obviously improved simultaneously. Therefore, the combination of the entransy dissipation extremum principle and the heat convection constructional optimization further illustrates the advantages of minimization of entransy dissipation rate for heat transfer optimizations.
The coagulation rate is an important parameter for colloids, which is very useful for evaluating the colloidal stability. Both static light scattering and dynamic light scattering are commonly used methods for measuring the coagulation rate. By using these methods, the light scattering properties of single particles and aggregates of two particles are needed. Therefore, one may need both the static and dynamic light scattering data to avoid the calculation of the relevant scattering properties. Usually, when only static or dynamic light scattering data are available, various approximations are used to solve the problems related to the light scattering properties of particles and aggregates. However, due to the limitation of size and shape of colloidal particles in these approximations, the results were not always satisfactory. Since the T-matrix method can be used to precisely calculate the characteristic of light scattering without approximation of particle size or shape, we use this method in the determination of coagulation rate in static or dynamic light scattering measurement in this study. The comparison of our results with those measured by simultaneous static and dynamic light scattering method confirms that the T-matrix method is suitable for the light scattering measurement of coagulation rate. Therefore, this study simplifies the coagulation rate measurement by light scattering methods and extends their applications.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
We have proposed a novel surface plasmonic nanolaser based on a nanowire/air gap/metal thin film hybrid structure to carry out theoretical research and simulation analysis. Opening an air groove in the MgF2 insulating layer, then making a nanowire embedded on the top of the air slot but maintaining a gap between the nanowire and the metal layer, thereby we produce a coupled hybrid plasmonic waveguide and a significant field enhancement effect. This structure enables the realization of an air gap. By simulating the modal properties and the lasing threshold of the hybrid plasmonic mode under different geometric parameters, the capacity of subwavelength scale with low propagation loss and high field confinement is demonstrated. Finally we achieve the nanolaser's optimal structure size. Compared with the general diffraction limit laser, this structure can reduce the physical size of the device and the physical mode. The proposed nanolaser could be easily integrated with various nanophotonic devices, and it may become an appealing candidate for future active plasmonic systems.
It is proposed that with a mini-cone target, an enormous number of high-energy collimated electrons can be produced, which may be used for fast ignition research. The effect of different laser and cone target diameters on high-energy electrons are studied with two-dimensional particle-in-cell simulations. When the open angle of the mini-cone is 10 degree, the number of generated hot electrons is relatively larger. With the increase of the open angle, both the energy and number of hot electrons decrease. When preplasma is added to the cone surface, the amount of hot electrons increases, while the peak energy of the hot electrons decreases. With the increase of the laser pulse duration, the number of high-energy electrons increases linearly.
Thomson scattering is one of the important methods of diagnosing parameters of the hot and dense plasma state that receive widespread attention. But the probe light wavelength for Thomson scattering is more limited to the visible or ultraviolet light, so the electron density that is copable to be diagnosed is much lower than the critical density of the driving laser. In comparison, soft X-ray laser as a probe is hopeful for diagnosing higher density of plasma. The experimental attempt of soft X-ray laser Thomson scattering has been carried out using Ne-like Ge soft X-ray laser generated on the SG-II high-power laser device. According to the scattering case, incoherent scattering and coherent scattering experiments were carried out, but it is unable to obtain the significant scattering spectrum. Theoretical analysis shows that the main reason may be the focusing power density of Ne-like Ge soft X-ray laser being not enough, in the experiments. By optimizing the experimental conditions, it is expected to obtain coherent Thomson scattering in the future.
Dielectric barrier discharge at atmospheric pressure not only behaves as a symmetrical period-one (SP1) discharge, but can also manifest itself as an asymmetrical period-one (AP1) discharge in certain ranges of parameters. In our study, a parallel electrode configuration is adopted and a series of discharge experiments are carried out in atmospheric helium at gap widths of 1, 4, 7 and 10 mm, respectively. The effects of gap width and driving voltage frequency on the symmetry of period-one discharge are investigated. Experimental results show that: AP1 discharge can be readily observed in a large range of parameters for the gap width and driving voltage frequency. AP1 discharge is prone to occur for a larger gap width; the critical value of the driving voltage frequency, beyond which the initial discharge is AP1 discharge, decreases as the gap width is increased. Results presented in this paper preliminarily verify the numerical simulations and the analysis which were previously reported in those papers studying the effect of gap width on AP1 discharge. Thus it can be conjectured that the AP1 discharge is not caused only by parameter asymmetry of discharge configuration, it can be also an intrinsic instability in terms of high frequency under certain parameters combination of gap width and driving voltage frequency.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
This paper describes the total ionizing dose effect on 0.18 μm narrow-channel NMOS transistors which are exposed to a γ-ray radiation. Electrical parameters such as threshold voltage, leakage current, trans-conductance, drain-source conductance, and subthreshold slope extracted from the I-V curves are analyzed pre-and post-irradiation. Results show that the threshold voltage, the trans-conductance, and the drain-source conductance are sensitive to radiation compared to wide-channel NMOS transistors–the effect we call radiation induced narrow channel effect(RINCE). The amount of oxide-trapped charges and interface states which would degrade the threshold voltage and leakage current is induced in the STI oxide. The gate oxide is insensitive to irradiation. Combining the structure and process of devices, we finally discuss and analyze the above phenomenon in detail.
A TiN coating with (111) and (222) preferred orientations was deposited on a Si(111) substrate by using reactive magnetron sputtering a Ti target. The deformation mechanism and fracture behavior of the coating are determined by nanoindentation and nanocratch experiments. The morphologies of the indentations and nanoscratch marks are revealed by scanning electron microscopy, in situ atomic force microscopy and optical microscopy. Local cracks of TiN appear around the indentation marks when the peak indentation displacement is below the critical value of 1000 nm. As the peak displacement exceeds 1000 nm, an interfacial fracture between the TiN coating and the Si(111) substrate is observed. Nonoscratch tests show that interfacial fractures are also induced by nanoscratch experiments under peak loads of 100 and 200 mN. The critical loads for interfacial fractures under 100 and 200 mN peak loads are equal to those under nanoindentation tests.
A series of Al-Ni-RE (RE=La, Ce, Y) amorphous ribbons were prepared. The crystallization behavior and primary phases were investigated using X-ray diffraction and differential scanning calorimeter, and their relationships with the alloy composition and atomic features were analyzed. Results show that if the topological instability parameter λ was modified using effective atomic radii, the metallic glasses in an Al-Ni-RE system can be classified into nanocrystalline, nanoglassy and glassy types according to their crystallization behaviors by two critical values of the modified topological instability parameter λ'. Linear relationships of onset temperature of crystallization and mixing enthalpy with λ' are also clearly revealed, indicating that λ' is closely related to the thermal stability of Al-Ni-RE metallic glasses.
In this paper, Fe-Fe50 wt.%Si diffusion couples are subjected to 1200℃ heat treatment in static magnetic field. Fe-Fe50 wt.% Si diffusion couples were prepared by vacuum casting technology and later sectioned and polished for scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies before heat treated. Microstructures of the treated samples which were polished first were analyzed by SEM and EDS; results show that the phase components of the interfacial intermetallic compound layers are FeSi phase layer and Fe-Si solid solution layer whether the samples were treated with or without magnetic field, and the layer widths in the samples treated with magnetic field are smaller than those without magnetic field. According to the parabolic law, the interdiffusion coefficients of the interfacial intermetallic compound layers were calculated and the interdiffusion coefficients of FeSi phase and Fe-Si solution under a field of 0.8 T are reduced by 26.7% and 34.1%. The Gibbs energy due to applied field was calculated, data analysis shows that the reduction of interfacial intermetallic compound layer coefficients is attributed to the decrease of frequency factor, not the activation energy. Decrease in layer thickness decrease is suggested to be related to the retardation of atomic diffusion resulting from the magnetic field, and a possible theory based on Larmor precession is given to explain this effect.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
The electronic structures, half-metallic and optical properties, as well as formation energy of pure LiZnAs, Mn-doped LiZnAs and Mn-doped LiZnAs with excess and deficient of Li are geometrically optimized and calculated by using the first principle density functional theory based on the full potential linearized augumented plane wave method. Results show that in the systems of Li(Zn0.875Mn0.125)As, Li1.1(Zn0.875Mn0.125) As and Li0.9(Zn0.875Mn0.125)As a 100% spin injectors is revealed, and the materials exhibit half metallic. The half metallic materials with excess and deficient of Li are more stable than Mn-doped LiZnAs. Excess of Li could improve the Curie temperature and conductivity of the material, and cause the formation energy of the system decrease. So the separation of spin and charge injection mechanisms may be achieved in LiZnAs semiconductor, and the magnetic and electrical properties of diluted magnetic semiconductor may be regulated respectively by Mn doping and Li stoichiometry. In addition, the dielectric function and the complex refractive index function in the low-energy region are found to be influenced by the stoichiometry of Li.
We report in this paper that low-voltage indium-zinc oxide (IZO) junctionless thin-film transistors (TFT) can be fabricated at room temperature, and the device stability performance influenced by oxygen pressure is studied. IZO junctionless TFT has a high mobility and novel structure, but the oxide channel layers are vulnerable due to the influence of oxygen and water molecules, which will lead to the degradation of the device stability. In this study, we fabricate transparent and conductive IZO thin-films at room temperature as channel layers, and source/drain electrodes by controlling the oxygen flow, and also analyze the effect of oxygen on the stability of oxide junctionless TFT. In order to operate at low-voltage (2 nanoparticle films as gate dielectric, which have electron double layers (EDL) effect and large gate capacitance, and the TFTs show excellent electrical performance with small operating voltage of 1 V, large on/off ratio(>106), small subthreshold swing(20 cm2/V·s). The study indicates that the resistivity of IZO thin-film fabricated in increasing oxygen content, leads the threshold voltage to drift in a positive direction, and makes operating mode of TFT change from depletion mode to enhanced mode.
First principle calculations predicted that Li atoms can be uniformly adsorbed on both sides of BC3 sheet without clustering. After the coverage of adsorbed Li atoms approaches 33.3%, Li+BC3 complex attains a largest hydrogen storage ability of 12.57 wt.%. Thermodynamic analysis confirms that at room temperature (300 K) and pressure in the range of 115–250 atm, Li+BC3 complex can have the hydrogen storage capacity mentioned above. These values satisfy not only the DOE (U.S.) requirement but also the security needs in application.
Enhancing the critical-current density of YBCO films is essential to gain a deeper understanding of the vortex pinning mechanisms and enable commercial applications of high-temperature superconductivity. Combined BaCeO3 and Y2O3 nanoparticles have been achieved to be co-doped in YBa2Cu3O7-x (YBCO) films by metalorganic deposition using trifluoroacetates (TFA-MOD). The formation of integrated nanoparticles increases the critical current density (Jc) of Y2O3/BaCeO3 doped-YBCO films while keeping the critical transition temperature (Tc) close to that in the pure YBCO films. YBCO film containing BaCeO3 and Y2O3 showed Tc value of 91 K and Jc value of 5 MA/cm2 at self-field (0 T, 77 K). The strongly enhanced flux pinning over a wide range of magnetic field may be attributed to the combined BaCeO3 and Y2O3 created by optimized TFA-MOD conditions.
The perpendicular magnetic anisotropy (PMA) of the CoFeB/AlOx/Ta structure and the AlOx/CoFeB/Ta structure with different thicknesses of both CoFeB and AlOx is studied. Magnetization curves show that the CoFeB/AlOx/Ta structure has a clear perpendicular magnetic easy axis while the AlOx/CoFeB/Ta structure does not. The cause of the asymmetrical phenomenon in the symmetric structures is analyzed. Dependence of the perpendicular coercivities on the thicknesses of CoFeB and AlOx shows that both of them can affect the strength of the PMA originating from the interfacial interaction. This work will be meaningful for the fabrication of the AlOx-based perpendicular magnetic tunnel junctions.
Raman spectroscopy has become a key way for characterizing and studying disorder in graphene, due to its nondestructive, rapid and sensitive technique. In this paper, ion implantation is used to produce the structural defects in single-layer graphene (SLG) and bi-layer graphene (BLG). The first- and second-order modes of ion-implanted SLG and BLG and their physical origins were studied by Raman spectroscopy. The dependence of dispersive frequency of first- and second-order modes in SLG and BLG on the excitation energy was discussed in detail. Results show that the ～2450 cm-1 peak is the combination mode of the D mode at ～1350 cm-1 and the D" mode at ～1150 cm-1.
In this paper, a series of Ca4-xY5.95 (SiO4)6F2: 0.05Ce3+, xMn2+ phosphors with an apatite structure were synthesized by the high-temperature solid phase method; their photoluminescence properties and energy transfer behavior were investigated. The obtained phosphors exhibit a broad excitation band ranging from 200 to 375 nm and also broad emission bands with two peaks centered at 408 and 602 nm monitored at 325 nm excitation, which originate from 5d→4f transition of Ce3+ and 4T1 (4G)→6A1 (6S) transition of Mn2+, respectively. The energy transfer from Ce3+ to Mn2+ was confirmed by spectral overlap phenomenon and decay curve measurements. Based on the analysis of the energy level structure of Ce3+and Mn2+, the existence of the energy transfer from Ce3+→Mn2+ was further confirmed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
We report the growth of single cubic phase Mg0.57Zn0.43O (MZO) alloy film through the method of metal organic chemical vapor deposition (MOCVD) and the relation between the quality and thermal stability of the alloy film after heat treatment. From X-ray measurement, we found that the quality of cubic MZO film was significantly influenced by the heating temperature. At 500-850℃, the crystallization and surface morphology of the alloy film were improved obviously as the temperature increased. Also, the blue shift of absorption cut-off edge, broadened band gap and maintained single cubic structure were found with increasing temperature. However, up to 950℃, mixed phases were formed in cubic MZO alloy film. For the photoresponse measurement of the MSM unit devices synthesized by the cubic MZO alloy film under 15 V bias, we found that the response peak of devices was around 260 nm, rejection ratio of UV/Vis was about 4 orders of magnitude, saturated responsibility was 3.8 mA/W and the value of dark current was about 5 pA.
The thermal decomposition of solid nitromethane (NM) is studied by ReaxFF molecular dynamics simulations to obtain the time evolution of the mechanism of NM under high temperature and pressure. It is determined that the initial decomposition mechanism of NM is dependent on pressure effect. In the 0–3 GPa pressure regime, the initial reactions is the C–N bond dissociation and the unimolecular rearrangement connecting between NM and methyl nitrite isomers; in the 4–7 GPa, the initial pathways of NM are the intermolecular proton transfer and C–N, C–O bond rupture. In the secondary reactions step, several fragments, like H2O, NO, NO2, HONO, play a role of catalysis. The product decomposition of NM contains many different structures of carbon clusters, and the configuration of cluster is dependent on pressure.
In this paper, based on the three-dimensional particle-in-cell (PIC) platform CHIPIC, a module of particle swarm optimization (PSO) is designed, and the code of PIC/PSO is developed. Then, the properties of multi-frequency output power are studied. Based on these properties, a class of optimization object functions is designed. With this PIC/PSO code and this class of object functions, single-frequency and dual-frequency RBWOs are optimized respectively. The optimization results show that both the single-and dual-frequency RBWOs can be optimized successfully with the corresponding object functions.
Ocean surface wind vector retrieval research on airborne fully polarimetric SAR (synthetic aperture radar) is of great significance for wind vector sounding under complex weather conditions near the coast. Starting from polarization scattering theory, we designed an ocean surface wind vector retrieval scheme for fully polarimetric SAR, by analyzing the relationship between fully polarimetric SAR sounding data and ocean surface wind vector. According to the high mobility and fully polarimetric two sounding characteristics of airborne SAR, firstly, we presented an ocean surface wind vector retrieval method based on maximum likelihood estimates for VV-polarized sounding data, and designed the flight experiment scheme. Secondly, we proposed an ocean surface wind vector retrieval method for VH-polarized sounding data, retrieved wind speed by VH-polarized ocean surface scattering model from optimum fitting with constraints, and calculated wind direction by CMOD5 geophysical model function. Using typhoon ''Haikui'' edge sounding data from airborne fully polarimetric SAR, we carried out the ocean surface wind vector retrieval experimental research. Results show that two wind vector retrieval methods can retrieve ocean surface wind vector under complex weather conditions without auxiliary information. Wind direction and wind speed retrieval root mean square errors of the former are 18.0°, 1.8 m/s, wind direction and wind speed retrieval root mean square errors of the latter are 9.3°, 1.2 m/s, and the accuracy of the latter is better than that of the former. The VH-polarized normalized radar cross section is more suitable for ocean surface wind vector retrieval under complex weather conditions, because it is independent of wind direction and radar incidence angle but has a linear relationship with respect to wind speed.
The amorphous silicon TFT (α-Si thin film transistor) were fabricated in a new structure, in which the ohmic contact layer (n+ layer) and the nitride silicon insulating layer for grid (G-SiNx) were stratified. Various factors which affect the electron mobility of α-Si TFT are studied using orthogonal test. With the increase in the number of n+ layer, the electronic mobility also rises. Besides, G-SiNx should be stratified into a rapid deposition film (GH) and a low-speed growing film (GL). The thickness of GL should be increased, with the thickness of GH reduced accordingly to achieve the electron mobility gradually increasing. Finally, based on the experimental results in the orthogonal combination experiments, the α-Si TFT mobility can stably reach 0.66 cm2/V·s, much higher than the traditional volume production data (0.29 cm2/V·s).
This paper proposes to use minus peak time of second derivative with respect to time on logarithmic curve of temperature versus time as a characteristic time for defect depth prediction in pulsed wave thermography. First, the paper introduces the basic principle of pulsed wave thermography, and constructs the theoretical relation between logarithmic minus peak second derivative time and the square of defect depth based on the solution of semi-infinite body. Then, two specimens of steel and aluminum were manufactured with flat-bottom holes to simulate defects. Thermographic image sequences of those two specimens were obtained by using pulsed wave thermography, and then the logarithmic minus peak second derivative time were extracted. The extracted characteristic time has a very good linearity relation with the square of defect depth, and this linearity could be used for defect depth prediction in practical applications. The advantages and disadvantages of the proposed method and the widely used logarithmic peak second derivative method are discussed.
Based on the density functional theory, influences of Al doping on stability and electronic structure of MgxTi1-x alloys and their hydrides were investigated. By calculating the formation energies of Mg-Ti-Al system, it is found that the best effect was obtained when the Ti-Al ratio was fixed at 1: 1, where the metal alloy was most stable, and was helpful to reversibly hydrogenate. Moreover, the partial substitution of Al for Ti atoms decreased the stability of the hydrides and improved the hydrogen storage properties. The analyses of the density of states, electron density and bond length showed that the improved properties of MgxTi1-x alloys and their hydrides with Al doping are due to the decrease in the number of bonding electrons and the weakening of Mg-H and Ti-H interactions in doped systems.
The direction of symmetry axis of parallel fracture set in fractured hydrocarbon reservoir affects the transmission of seismic waves markedly, so a medium named fracture-induced TTI (tilted transverse isotropy) double-porosity medium is studied here to discuss the effect of different dip and azimuth angles of a fracture system. Based on the theories of fracture-induced HTI (horizental transverse isotropy) double-porosity medium, the softness and dispersion matrixes of fracture-induced TTI double-porosity medium are derived with the application of Bond transform, and finally, single-order velocity-stress equations are obtained. Furthermore, numerical simulations in xoz plane of 2.5 dimensional vector wavefield are carried out by the method of high-order staggered-grid finite-difference under perfect matched layer (PML) boundary conditions. The results show that the dipand azimuth angles of fractures have great impacts on seismic wave propagation, since the angles can cause the phenomena of shear wave splitting and, in the two-layer model of fracture-induced TTI double-porosity, converted shear wave splitting and shear wave sub-splitting. All of these increase the complexity of seismic wavefield and will lay a foundation of further studies on seismic wave propagation in actual earth layers.
With respect to the whole of two elemental waves in ocean surface, capillary and gravity waves, a deterministic, rich and fundamental theory of 3-4-5-wave resonance and conservation for ocean surface waves in a finite depth is developed, which presents fully the preciseness, symmetry and completeness as compared with a variety of the classical, modern results, and provides an indispensable basis for the succeeding and universal statistical theory of ocean wave turbulence.
China's Loess plateau, as one of the areas in the world, is vulnerable to ecological environment and sensitive to climate change. The characteristic of land surface process has been changing in this area, and it affects the formation and evolution of regional weather and climate. However, limited by observational land surface data, exchange process variation of the surface energy of the Loess plateau and its mechanism of response to climate change is limited. In this study, we combine the observed experimental data with the land surface model simulated data, test the previous four land surface models. It shows the CLM is reliable in Loess plateau. Then we use the observed data and model simulated data to analyze the variation of regional climate and the characteristics of land surface energy exchange, and discuss the effect of climate change on land surface energy exchange. It shows that Loess plateau is warming and drying in recent decades. It induces the increase in solar radiation, surface reflected radiation and surface longwave upward radiation. This makes the net radiation decrease. Correspondingly, surface latent heat flux, sensible heat flux and soil heat flux all have a decreasing trend. But the distribution ratio of components of surface heat flux is basically unchanged. In addition, the annual variation of sensible heat flux is controlled by solar radiation, and latent heat flux is controlled by solar radiation and precipitation. The annual variation of each component of surface heat flux is sensitive to precipitation, not sensitive to temperature. The climate acidification affected surface energy balance farmore than temperature rise.
Based on the global Palmer drought severity index (PDSI) data and monthly precipitation data from China, using linear trend analysis, comparative analysis and EOF methods, the spatiotemporal evolution of the droughts and floods over China during 1961–2010 has been analyzed. Results show that: The decadal spatial distribution of PDSI in spring is similar to that in year-round. The regional differences of PDSI in summer and autumn are obvious, especially in autumn. According to the linear analysis, climate in North China, Northeast China, Southwest China, South China and East China is becoming dry obviously; while the west of Northwest China is becoming wet. The PDSI in summer from 1961 to 2010 is also analyzed by experience orthogonal function (EOF). Results show that droughts and floods occur frequently in China since the 1980s and the intensity of droughts and floods is also increased, especially droughts in the North China, Southwest China, Northeast China and floods in East China.
The timing equation is the basic theory of dealing with the observable data of pulsar. The pulse timing model is studied; the transformation equation of pulsar photon time of arrival in 1PN approximation is derived, the existing transformation equations are compared and analyzed; the transformation of the proper time from the spacecraft to TCB is also obtained. The process dealing with the observable data of RXTE is achieved by software, the pulsar period is estimated and pulse profile is replicated, the validity of timing equation is approved. The result of software is compared with that of Heasoft, the reason of difference between them is analyzed. Finally, the effects of the planet ephemeris error and the pulsar ephemeris error on data processing are achieved.
In order to increase the detection speed and to improve the detection rate in low signal-to-noise ratio, a novel detection algorithm for pulsar integrated pulse profile is proposed based on S-transform. We prove that the local S-transform spectrum of Gaussian white noise follows chi-square distribution with two degrees of freedom in this paper, and based on this, threshold processing is operated on the S-transform power spectra of cumulative signal; then, the total energy of the time-frequency power spectral after threshold processing is accumulated to construct the detecting statistics to obtain the statistic decision. Moreover, the time-frequency power spectra after threshold processing can also be used to measure the time delay of pulsar signal. The simulation result verifies the effectiveness of the proposed method which is superior to a similar method based on the Gaussian distribution; in addition, it can give the time delay with a certain accuracy.